title: Synthesis of 4-methylumbelliferyl α-d-mannopyranosyl-(1→6)-β-d-mannopyranoside and development of a coupled fluorescent assay for GH125 exo-α-1,6-mannosidases.
abstract: Certain bacterial pathogens possess a repertoire of carbohydrate processing enzymes that process host N-linked glycans and many of these enzymes are required for full virulence of harmful human pathogens such as Clostridium perfringens and Streptococcus pneumoniae. One bacterial carbohydrate processing enzyme that has been studied is the pneumococcal virulence factor SpGH125 from S. pneumoniae and its homologue, CpGH125, from C. perfringens. These exo-α-1,6-mannosidases from glycoside hydrolase family 125 show poor activity toward aryl α-mannopyranosides. To circumvent this problem, we describe a convenient synthesis of the fluorogenic disaccharide substrate 4-methylumbelliferone α-d-mannopyranosyl-(1→6)-β-d-mannopyranoside. We show this substrate can be used in a coupled fluorescent assay by using β-mannosidases from either Cellulomonas fimi or Helix pomatia as the coupling enzyme. We find that this disaccharide substrate is processed much more efficiently than aryl α-mannopyranosides by CpGH125, most likely because inclusion of the second mannose residue makes this substrate more like the natural host glycan substrates of this enzyme, which enables it to bind better. Using this sensitive coupled assay, the detailed characterization of these metal-independent exo-α-mannosidases GH125 enzymes should be possible, as should screening chemical libraries for inhibitors of these virulence factors.
authors.affiliation: Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1S6, Canada.
authors.forename: Lehua
authors.initials: L
authors.lastname: Deng
authors.forename: Polina
authors.initials: P
authors.lastname: Tsybina
authors.forename: Katie J
authors.initials: KJ
authors.lastname: Gregg
authors.forename: Renee
authors.initials: R
authors.lastname: Mosi
authors.forename: Wesley F
authors.initials: WF
authors.lastname: Zandberg
authors.forename: Alisdair B
authors.initials: AB
authors.lastname: Boraston
authors.forename: David J
authors.initials: DJ
authors.lastname: Vocadlo
mesh_terms: D003016:Clostridium perfringens / Q000201:enzymology; D004187:Disaccharides / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D057075:Enzyme Assays; D005456:Fluorescent Dyes / Q000737:chemistry; D007700:Kinetics; D013296:Streptococcus pneumoniae / Q000201:enzymology; D013379:Substrate Specificity; D014468:Umbelliferones / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D043323:alpha-Mannosidase / Q000737:chemistry / Q000378:metabolism*
chemical_list: C586295:4-methylumbelliferyl alpha-D-mannopyranosyl-(1-6)-beta-D-mannopyranoside; D004187:Disaccharides; D005456:Fluorescent Dyes; D014468:Umbelliferones; D043323:alpha-Mannosidase
keywords: Coupled enzyme assay; Disaccharide; Glycan catabolism; Glycoside hydrolase; Mannosidase; N-glycan; β-Mannose